What is a requirement for warning traffic when a vehicle is stopped on the road?

Using emergency flashers is the correct requirement for warning traffic when a vehicle is stopped on the road. Emergency flashers, often called hazard lights, serve as a visual warning to other drivers that a vehicle is not moving, which could be due to mechanical issues or other emergencies. This alert is crucial for maintaining safety on the road by informing other road users to approach with caution and be prepared to maneuver around the stopped vehicle.

While turning off the engine, setting off an alarm, or doing nothing could theoretically be options in specific contexts, they do not fulfill the critical need for clear communication to other motorists about the vehicle's status. Emergency flashers actively convey that the vehicle is a potential hazard, which is essential in preventing accidents and ensuring the safety of all road users.